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Weed Control Guide
The Weed Business
Killing weeds is big business. How to get turf to thicken up and be weed free are the most common questions I get. Weeds bother people more than any other pest it seems. As the late Charles Walters said, “weeds affect our psyche”. It’s ironic but weeds have great value. Mother Nature uses them in spots where other plants won’t grow and improve the soil to allow for higher successional, plants to grow. Weed seeds are all over the place, in all soils and can live in the soil for years and years just waiting for a chance to germinate. When they do start to grow, it is for a reason - usually to cover bare soil. Therefore, the primary control of weeds is to eliminate the conditions which create the need for weeds.
Weeds rarely invade a high-quality lawn. All the money in the world can be spent on weed-controlling products and techniques, but if the lawn is not maintained properly, the weeds will return. Once a weed is growing it must be removed either mechanically by digging or by spraying. The underground parts of some weeds are capable of growing new plants so the rhizomes (underground stems) of those plants must be removed. That’s the case with Bermuda and other grasses. Annual weeds do not have the reproductive laterally ground stems.
The "chemical users" say the rule of thumb is that the weed must be actively growing for it to be controlled. Also, the younger a weed is, the easier it is to control. Old weeds are much tougher to kill but the organic sprays work whether the weeds are vigorously growing or not.
Types of Weed Control
Commonly available weed controls are divided into two groups - those that kill the weed seed as it germinates (pre-emergent herbicides) and those that kill the weed after it germinates (post-emergent herbicides).
Toxic products and Natural Organic Products Available On The Market.
In the toxic chemical category, there are herbicides like broadleaf herbicides like 2-4, D and Roundup. They are toxic to soil, animals and people and harmful to the environment.
Recommended natural organic products include 10% pickling vinegar, Good Natured 20% vinegar and Sycthe. They are made mostly of vinegar, citrus and fatty acid.
Pre-Emergent Weed Control
With pre-emergent weed controls, a product is applied evenly over the lawn and forms a barrier at the soil surface. The synthetic products such as Scott’s Bonus S use harsh chemicals. As you will notice right on the label, it contains a herbicide called atrazine that is damaging to your shrubs and trees.
Quotes from the Bonus S package instructions:
"Do not use under trees, shrubs, bedding plants or garden plants."
"Do not apply on or under the branch spread (rootzone) of trees, shrubs, bedding plants, flowers or garden plants."
"Do not apply by hand or hand-held rotary devices."
"Do not apply this product in a way that will contact any person either directly or through drift."
"Runoff and drift from treated areas may be hazardous to aquatic organisms in neighboring areas."
"This product is toxic to aquatic invertebrates."
Post-Emergent Weed Control
Post-emergent chemicals are used to kill weeds after they come up. These weeds, are divided into two groups – grasses and broadleaf.
Natural Weed Control
The natural way to control weeds is to build the soil by increasing the organic matter and most weeds won’t be a problem. In the interim, hand pull problem weeds, spot spray with vinegar-based herbicides and apply corn gluten meal at 20 lbs./1,000 sq. feet spring and fall prior to seed germination.
For winter weeds, spray between Christmas and New Years with vinegar formula. This technique works fairly well any time during the winter when the summer grasses are dormant.
Weed Control in Beds
This is the easy part. The best program is to start with clean beds, mulch them properly and hand pull any weeds that pop up.
There are some specific controls that work in certain conditions. Weeds in beds can be killed by removing the tops and then covering the problem area with 1/2" of compost followed about 5 layers of newspaper or 1 layer of cardboard. Wet it all down and cover the paper with 2-4" of shredded native mulch. Spot spray any weeds that manage to come through with the vinegar herbicide.
Vinegar Herbicide Formula:
1 gallon of 10% vinegar
1 ounce orange oil or d-limonene
1 teaspoon liquid soap or other surfactant
Add molasses at 1 tablespoon per gallon to the vinegar formula
Organic herbicides available commercially include the following:
Vinegar products – Good Natured and Fleischmann
D-Limonene product - Good Natured and Medina Orange Oil
Fatty acid product – Scythe
The only selective organic herbicide available currently is the Agralawn Crabgrass Killer
. It can be used any time of the year to kill crabgrass, clover, henbit, Illinois bundleweed, false strawberry and other fuzzy leafed grasses and broadleaf plants without hurting the turfgrass.
Weeds in Paved Areas
Weeds can be controlled with non-toxic products. Forget using black plastic, toxic chemical herbicides, salt and bleach. Remember one of our primary rules – do nothing to harm the life in the soil. Bleach and toxic chemical herbicides are poor choices, but there are some good ones.
In gravel, in cracks and joints in concrete and other paving systems, weeds can be controlled with non-toxic products. Use the organic herbicides and vinegar based mixture mentioned above. These organic herbicides, just like the toxic chemical products, only work on actively growing plants.
To keep the weeds out of a decorative or utility gravel area, the best approach is to design them out from the beginning or use organic products later to kill the weeds. Salt, toxic herbicides and bleach should never be used because they contaminate the soil long term. They also leach into the water stream. To head off the problem, install the gravel in a thick layer – 6-8” after scraping away all grasses and weeds.
For additional control, add a layer of white caliche rock before putting the gravel on top. Any weeds that grow through the gravel can be sprayed and killed with organic herbicides.
Grassy Weed Control
These are the hardest of the weeds to control because there just aren't many non-toxic chemicals or organic products available that can selectively remove a grassy weed from among the desirable turfgrass plants. One of the few select organic weed controls is AgraLawn Crabgrass Killer. It is a potassium bicarbonate and cinnamon product that works well when applied per label instructions. It is effective on crabgrass, basket grass, chickweed, clover and other weeds.
Broadleaf Weed Control
There are several toxic chemicals that are recommended for controlling broadleaf weeds in any lawn. These chemicals are usually mixtures of several chemicals. They are very toxic, dangerous and should not be used. The organic contact killing herbicides will work but are non-selective. Care must be taken to avoid spraying desired plants. The grassy weed control products mentioned above can also be used on broad leaf weeds.
Not a grass or broadleaf weed, nutgrass
(technically nutsedge) is one of our most troublesome weeds. We used to say that there's no good organic or toxic chemical solution for nutgrass. On the toxic chemical side, that’s true. The commonly recommended chemicals are Image and Manage. Most everyone in the landscape industry agrees with me that Image doesn't work on one of the most common species. Manage works better but will severely damage or kill your trees.
I have had luck and others have reported success killing nutgrass with kindness. Mow, clip or pull as often as you can and apply a heavier than normal application of dry molasses. Use about 20 lbs. per 1000 sq. ft. and repeat in two weeks. The mixed products that contain molasses, and cornmeal will also help. The idea here is to stimulate a furious level of biological activity aimed at rotting the crowns of the undesired plants. Nutgrass (nutsedge) likes moist, anaerobic soil. As a result, improving drainage and having aerobic soil helps, but the complete cure is molasses.
The idea here is to stimulate a furious level of biological activity aimed at rotting the crowns of the undesired plants. It works. Liquid molasses also works. Drench problem spots with liquid horticultural molasses at ¼ to ½ cup per gallon of water. Start with about a gallon of drench per 9 – 10 sq. ft. This simple technique fires up the microbes in the soil and the nutgrass simple fades away.
Other remedies include: Remove the weed physically with mechanical devices. For turf, overseed problem areas with ryegrass in the fall. Applying corn gluten meal in the spring at 20 pounds per 1,000 square feet prior to seed germination is also helpful. An important point to remember is that nutgrass (nutsedge) grows primarily in wet anaerobic soil. Applying hydrogen peroxide, the kind at the drug store, full strength to the problem areas can help. Also let the area dry out better between watering, improve soil health, improve drainage and help the soil to drain better.
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